Structural Elucidation of the 5HT1a Receptor-G Protein Interface The serotonin1a (5HT1a) receptor is centrally involved in various human disorders including depression, anxiety, obsessive-compulsive disorder, and migraine headache. The receptor is a member of the superfamily of seven transmembrane domain, G protein-coupled receptors. By agonist stimulation of receptor, G protein is activated, which in turn regulates cellular effectors such as adenyl cyclase. Through these events, informational signal is transduced into cellular changes which underlie drug effect at the biochemical level. In this project, the focus is on events surrounding the key interaction between receptor and G protein. A peptide from the transmembrane 5/intracellular loop 3 region of the human 5HT1a receptor, and substitution and truncation derivatives of this peptide are used as probes of the receptor/G protein interface. The peptide's abilities to activate inherent properties of the G protein, such as incorporation of GTP into the G protein, and GTPase activity, are quantified. By cross-linking, regions of the G protein responsible for coupling to the receptor will be identified. Finally, selected peptides which have demonstrated outstanding activity in these tests will be used for high resolution spectral studies. Circular dichroism of the peptides will be measured in solution to determine conformations of the peptide as it approaches G protein prion to coupling. Once coupled, multi- dimensional NMR of the peptide/G protein complex will determine conformations which lead to G protein activation. Information gathered in these experiments will form the basis for development of models of 5HT1a receptor peptide/G protein interaction. In the long range, structural lessons learned from the human 5HT1a receptor/G protein system will add to growing knowledge of receptor/G protein events in the receptor superfamily. Better structural and biochemical understanding of these receptors will help in elucidating receptor pathology in detail, which in turn should assist in better understanding of important human disease processes. Additionally, development of understanding of at receptor/G protein interactions will potentially lead to therapeutic approaches targeted at pathologies in the sequence of signal transducing events.